It is known to employ digital cameras to capture infrared information from a scene having specular surfaces, for example a part on an assembly line, or a specimen in a microscope. It is also known to use a source of artificial infrared illumination to aid in the capture of such images. A problem occurs in such image capture situations because the specular reflections of the source of infrared illumination wash out the detail in the image in the neighborhood of the specular reflection. Furthermore, in applications such as surveillance, it would be preferable if the source of such illumination remained unnoticed by the subject. Conventional flash systems capable of producing substantial infrared light also produce appreciable quantities of visible light. If the visible light from such a flash is filtered to produce an infrared flash, the resulting flash apparatus is inefficient, since a considerable portion of the energy produced by the flash is wasted. In applications such as machine vision and microscopy, it is desirable that the source of illumination be highly uniform and extended in space (non point source) to minimize the intensity of specular reflections. However, in applications where the object needs to be close to the lens, there is scant room for an extended light source. Therefore, it is also desirable for the light source to be compact, a requirement that is in apparent conflict with the need for the light source to be extended.
U.S. Pat. No. 4,866,285, issued Sep. 12, 1989, to Simms discloses a light source for an infrared film camera having one or more infrared diode light sources. It has been found that due to the point source nature of the infrared diodes, the illumination from such a light source is non-uniform at the subject and the point source nature of the diodes causes intense specular reflections from an object having specularly reflecting surfaces. There is therefore a need for an improved, energy efficient, uniform source of infrared illumination for infrared electronic photography.